The present invention relates in general to trocars for use in endoscopic, laparoscopic, and arthroscopic surgery, and in particular, to trocars that employ a moveable shield to establish a surgical port in an internal body cavity.
Trocars are generally assembled from two primary components, a cannula tube and an obturator. The trocar assembly is inserted through the skin to gain access to a body cavity so that endoscopic surgery can be performed. The trocar is placed against the outer skin of a patient, and pushed through the layers of skin, fat, muscle, and fascia until the trocar enters the body cavity. Once the trocar is properly positioned, the surgeon removes the obturator so the cannula can be used as an access port for endoscopic instrumentation.
The trocar and obturator assembly, while of great benefit, could inadvertently penetrate organs or other body structures during insertion. The addition of a moveable shield to envelop the piercing or cutting tip of the trocar was a breakthrough concept. The shield consists of a spring loaded generally tubular member interposed between the piercing or cutting tip and the trocar cannula. In the unbiased state, the shield covers the piercing tip of the obturator. When the distal shielded end of the trocar is pressed against the skin of a patient, the shield retracts to expose the piercing or cutting tip. When the body layers are penetrated, the force on the shield lessens and the shield spring biases the shield distally to envelop the piercing tip. Any further distal motion into the body cavity results in the blunt shield contacting the underlying organs or structures, rather than a cutting or piercing tip. A trocar describing such a shield can be seen in U.S. Pat. No. 4,535,773.
Typically, the piercing or cutting tip of a trocar has been of a conventional pyramidal or conical shape. While the tip is effective in penetrating tissue, the use of a flat, razor blade has been found to offer less trauma to tissue during penetration and is described in U.S. Pat. Nos. 5,314,417 (Stephens et al.) and 5,609,604 (Schwemberger et al.). The flat blade, as described in these patents, is shielded within a tapered bullet shaped shield that offered additional improvements in accordance with the principles of Deniega, as found in U.S. Pat. No. 5,066,288. The combination of a flat blade that produces a diametral slit in tissue with a shield shape that dilates the tissue as it penetrates, was found to reduce the force of penetration, improve the shield response time, and improve healing.
With the flat bladed shielded trocar, new levels of safety and performance were reached. However, there are disadvantages, such as an increased force to penetrate, caused by the need to overcome the shield spring force to expose the piercing tip. It would therefore be desirable to provide a shield with a precock feature that enables the shield to be retracted and locked in an armed position, with the piercing or cutting tip exposed. This precooking action would desirably compress the shield biasing spring, arm the shield in a ready to deploy condition, and reduces the force of penetration. A trocar describing such a shield, with a pyramidial tip, is described in U.S. Pat. No. 5,431,635 (Yoon).
While the precooking shield with a pyramidial tip addressed the conventional shield retraction problem, it did not provide the means for the surgeon to make the initial skin incision at the trocar insertion site. This incision is generally made in the skin to reduce the penetration force and requires the use of two surgical instruments to make a trocar insertion, a trocar and a scalpel. The scalpel, or surgical sharp, poses a handling risk to surgical personnel as surgical gloves can be inadvertently cut or nicked during the exchange, exposing the handler to bloodborne diseases. The scalpel is passed back and forth each time a trocar, or surgical access port, is inserted, providing multiple chances for a mishap. Although there is a discussion in the Stephens et. al '417 patent concerning the use of a flat blade to incise internal tissues, there is no discussion concerning the availability or the desirability of using the flat blade of the trocar to initially incise the skin to avoid the use of a surgical sharp, and thus avoid the disadvantages attendent with this type of instrument.
Significant advances have been made in the development of surgical penetration instruments, and the methods of their insertion, but there are still risks to surmount. It would be advantageous if there was an instrument that combined a precocking shielded trocar with a surgical scalpel blade so that one instrument could be used, with increased safety, to both incise and penetrate tissue at a surgical site.